In communications systems which transmit data for visual display, by some means such as phase shift keyed sequences, and which also transmit voice messages it is desirable to mute the receiver during the transmission of the phase shift keyed data sequences so that the tones produced by these sequences are not audibly reproduced in the receiver. A system of this type is described in U.S. Pat. No. 3,906,445, entitled "Alphanumeric Terminal for a Communications System" and assigned to the same assignee. In this system the phase shift keyed data is transmitted first and is followed in the same transmission by any voice messages it is desired to transmit. Since the tones produced by the phase shift keyed data can be extremely irritable, many attempts have been made to mute the receiver during the data sequence without losing any of the voice message. Prior art structures include general data/voice discriminators which operate on the use of the fast Fourier transform. However, these circuits take a minimum of a few seconds to make a positive identification of either voice or data. Therefore, annoying tone bursts may still occur before muting and portions of the voice message may be muted.